Peter Laidler the Senior British Army Armourer in the The UK and author of the "The Armourers Perspective .303 No.4 (T) Sniper Rifle and the Holland & Holland Connection contacted me by email. He wanted to know "WHY" I always talked about tight headspace on the Enfield rifle and then proceeded to give me a polite earful on headspace and the Enfield rifle. Mr. Laidlers main point was simply this, the more clearance between the rear of the cartridge case and the bolt face the less bolt thrust is applied to the bolt. Meaning the cartridge case stretches and acts like a shock absorber and thus reduces the bolt thrust and the dwell time the force is applied to the bolt. In plain English this why the headspace increases on rifles over time and just one reason why military rifles have longer headspace settings.
I have necked sized only for practice ammunition "BUT" you MUST grease the rear of your locking lugs or the tight fitting case will cause wear and possibly gauld the locking lugs. Next, the neck sized case is in direct contact with the bolt face and delivers the total bolt thrust to the action. Bottom line, I neck size my .303 British cases BUT I do not load them hot, my hotter rounds have good shoulder bump that lessons the bolt thrust.
Neck sizing depends on the type shooting you will be doing meaning off the bench and the type rifle you will be shooting meaning WHAT TYPE METAL the rifle is made from and understanding what bolt thrust means. Now ask yourselves WHY the Enfield rifle had replaceable bolt heads and why the headspace would increase. Today modern firearms are made of very good steel and can take more pounding than the older milsurp rifles "BUT" they still don't like being abused. The Australians perfected the conversion of the No.1 Enfield rifle to 7.62 NATO with higher grade EN steel. When standard No.1 Enfield rifles were chambered to 7.62 without upgradeing the bolt and bolthead to EN grade steel the test rifles headspace increased to over maximum and the bolt heads cracked after very few rounds had been fired. So again what type rifle are you neck sizing for and how hot are your loads?
I full length resize the majority of my reloads because I'm not spending money on Lapua brass and the the brass I do use is not perfectly made and has defects in case wall thickness which effects case alignment and runout. By full length resizing you reduce the effects the case has of misalignment of the bullet with the bore. So the QUALITY of your brass and your chamber play a big part in your accuracy, so how many of you have custom made rifle with tight neck chambers and neck turn your brass. Meaning there are things competitive shooters use with expensive hand crafted rifles and things you do with off the shelf factory rifles and standard grade brass.
If you look at the photo below you will see the Hornady cartridge case concentricity gauge in the back left of the photo, this gauge lets me "bend" cases with excess neck runout. Meaning a high percentage of standard grade brass will have runout in excess of .003.
Neck sizing and full length resizing covers a lot of area and you have to know how to get the best mileage out of both methods and why you are doing it and its effects. And if you do not have gauges to check the quality of your case anything you say here is just guesswork and reading too many comments by so called online "experts".
In closing Saddam Hussein's cat preferred neck sizing also but that is just one opinion.................